nana::form
Defined in header
class form;

The form widget represents a popup window. Overall it is a root widget(see Overview of widgets) which attaches the OS/Windowing system native window.


Public base classes
widget_object : public widget

Member typedefs

Member functions

Example
When you define an object of form widget, the UI element start immediately. 
#include 
int main()
{
        using namespace nana;
        form fm;
        fm.show();      //It's OK, because UI was started when it constructed.
        exec();
}

Create a modal form.
A modal form is to block the routine and only interacts with the specified form until the specified form is closed. Generally, a modal form is created during an event handler function, such as click a button and open a form to ask user for inputs. 
int main()
{
        using namespace nana;
        form fm;
        fm.events().click([&fm]{
                form fm_modal(fm);              //A owner is required for the modal form
                fm_modal.modality();    //It shows the fm_modal and enters a routine for modal form.
                std::cout<<"modal form was closed"<

See also
Overview of widgets, nested_form